Teleview,
Once again thanks for the very comprehensive answer. Answers were all very clear, but still having a hard time with the two columns that have "db" figures. Which means what? In particular to what you wrote above.
My only stations of concern are "yellow" and above and then only about 6 of them. The db numbers there mean little to me in either of the two columns. What is the difference beteen the columns?
I can get the antenna higher, but likely not to 90 feet. 40 is easy enough, and I could probably get to 70 or so AGL, but 90 starts to get difficult for me to deal with.
I will try the experiments you mention above as well, but kind of trying to figure out about where my "finish line" is and mostly what the two db columns mean to me.
My closest tree in direction I need (50 mag) is 80 feet away from antenna, and I can get that back further, but when is it enough? Would prefer to not clear a hole (path) through my entire lot that goes back about 1/4 mile in that direction. If what I think I interpret from what you wrote above, everything I want (yellow and above) is a positive number in one of the two columns, but the other column is negative. My trees back there are all about 90-100 AGL, but lot slopes down quite a bit back there, so I get some help with height, probably not enough to clear them completely though, short of clearing a path through the entire lot.
My only interest channels are all yellow lines and above
ABC
CBS
NBC
FOX
Channel 20
Channel 50
Don't at all care about any of the others.
Thanks once again, and very much appreciated !!!!